The effects of new antiarrhythmic agents will be studied using diseased tissue preparations. Microelectrode studies will be carried out in infarcted tissues excised from the hearts of animals following myocardial infarction. This will allow us to study the electrophysiologic mechanisms of ventricular arrhythmias and the modes of action of new antiarrhythmic agents under conditions which mimic the changes encountered in clinical myocardial infarction. The changes in excitability and conduction of the ischemic bundle branches will also be investigated in vivo, and the changes will be correlated with the occurrence of bundle branch block and re-entrant ventricular arrhythmias. These studies will improve understanding of ventricular arrhythmias and lead to improved methods of treating ventricular arrhythmias and decreased fatality of patients with myocardial infarction.